Understanding the phase change behavior and thermal properties of cryoprotective agents (CPAs) in biological solutions is essential for enhancing the success of cryopreservation and biobanking. In this study, the phase change behavior and thermal properties of normal saline added with trehalose or l-proline were investigated using differential scanning calorimeter (DSC) and cryomicroscope during freezing and warming. The addition of trehalose or l-proline can eliminate the eutectic formation in normal saline. Trehalose had significantly lower latent heat release than l-proline does at a high concentration of 1 M (P < 0.05), while unfrozen water content of trehalose is significantly lower than that of l-proline at all the concentrations (P < 0.05). It was also found that addition of 0.2 M, 0.3 M and 1 M trehalose can achieve partial vitrification in normal saline and that the glass transition temperature rises along with the increase in concentrations of trehalose. However, no vitrification was observed in normal saline with l-proline at any concentrations. Besides, rates of ice crystal growth in normal saline added with trehalose are slower than those in normal saline with l-proline at the same concentrations. These results suggest that both trehalose and l-proline can act as CPAs by avoiding eutectic formation and inhibiting ice formation in normal saline for cell cryopreservation. It could be useful for CPA selection and designing in the future.
Keywords: Cryomicroscopy; Cryopreservation; Cryoprotectants; Differential scanning calorimetry; Eutectic crystallization; Vitrification.
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